facefault

Often seen in anime, this is when someone immediately falls face-first onto the floor with a loud "CLUNK" sound, often as the result of being the victim of an atrociously bad joke.

For example, in episode six of the original Tenchi MuyoOAV, Washuu declares that there is one thing they can do to help in the life-or-death struggle between Tenchi and the villain. Mihoshi asks earnestly what it is. Washu pulls out paper fans and starts cheerleading. Mihoshi facefaults.